The American Cancer Society estimates that 62% of all cancers could be prevented altogether through lifestyle change. Despite good intentions, people's attempts to alter their behaviors known to increase cancer risk - related to diet, physica activity, tobacco and alcohol use - often fail, which ultimately increases their risks for various cancers. In response to NCI's Provocative Question 4, the overarching goal of the proposed research is to investigate the role of positive emotions in facilitating successful lifestyle chang, defined as long-term adherence to cancer- preventive behaviors (e.g., nutritious eating, physical activity, tobacco, and alcohol use). An innovative upward spiral model of lifestyle change integrates multiple streams of research in basic behavioral and brain sciences to position positive emotions as key active ingredients that not only seed non-conscious motivational pulls toward newly-adopted cancer-preventive behaviors, but also reshape key biopsychosocial resources in ways that increase the subsequent positive emotion yield of multiple cancer-preventive behaviors, creating a self- sustaining dynamic system. A longitudinal, dual-blind, placebo-controlled field experiment tests this new model by targeting three Specific Aims. These aims are: (1) to identify biopsychosocial resources that moderate the link between cancer-preventive behaviors and their positive emotion yield; (2) to test whether and how positive emotions, experienced in daily life, produce a psychological propensity for wellness through the combined presence of (a) increases in non-conscious motives for cancer-preventive behaviors and (b) increases in biopsychosocial resources; and (3) to test whether positive emotions and a psychological propensity for wellness predict increasing and sustained cancer-preventive behaviors and improved health-related outcomes at 18-month follow-up. The proposed study tests the novel upward spiral model in daily life with densely repeated measures and physiological, behavioral, endocrine, and self- report indices of health-related outcomes. This program of translational research stands to reshape public health interventions and unlock hidden opportunities to drastically reduce the incidence of cancer.